Prevention of venous thrombosis and pulmonary embolism is one of the major concerns of clinicians nationally. Pulmonary embolism is estimated to be the third most common cause of death in the United States. Hospitalization due to venous thrombosis and pulmonary embolism are associated in ranges of 300,000 to 600,000 a year and results in as many as 50,000 to 200,000 deaths a year as a result of pulmonary embolism.
Patients undergoing various types of surgical procedures as well as trauma are at high risk for developing deep vein thrombosis (DVT) and pulmonary embolism (PE). Averages demonstrate that the orthopedic patient population appear to be especially prone to thrombosis with highest risk in those patients with hip, tibial and knee fractures.
Factors contributing to the development of deep vein thrombosis include vascular stasis, coagulation changes, and blood vessel damage. It is generally believed that slowing of the blood flow or blood return system from the legs during and after surgery, is the primary factor related to the development of DVT. It appears that this slowing has its greatest effect during the intraoperative phase, but is also of concern during the postoperative period.
Recent evidence, documented by Kakkar, V. V.: Prevention of venous thrombo embolism., Clin. Haemat. 10 (1981), 543-582, has identified a possible "fibrinolysis shutdown" contribution to clot formation. These factors are notably combined in orthopedic operations on the lower-limb which are recognized high risk procedures.
The body's normal physiologic mechanism to return fluid to the heart is based on muscle contraction of the lower extremity. It is the general belief that contraction of the posterior musculature including gastrocnemius/soleus muscles aid the return of fluid from the deep venous sinus in the lower extremity. It is the pumping mechanism of the muscles by changing the length and breadth of the structures that compress the venous sinus evacuating the pooled blood in those veins.
It was the belief that muscle contraction assisted venous return from the lower extremities that became the primary factor for initial research in use of electro stimulation of the lower extremities during surgical procedures to prevent venous stasis. The earliest use of galvanic stimulation for stasis prevention was by Doran. British Journal of Surgery, 511:486, 1964. Doran's method utilized calf muscle stimulation with galvanic current at 30 impulses per minute to promote fluid return of the lower extremities. This stimulation produced strong plantar-flexion of the foot throughout the operative procedure. A galvanic current was utilized to overcome the anesthetic agents used by anesthesiology which block the myoneuro junction of the muscles. Due to the operative theater, the unit was positioned on the left side of the patient, thereby stimulating only the left lower extremity.
There have been various researchers addressing the use of electrical stimulation to reproduce the physiologic activity of the calf muscles for the prevention of post operative thromboembolic complications. Original work by Nicolaides A. N., Kakkar V. V., and Field E. S. et al.: Optimal electrical stimulus for prevention of deep vein thrombosis, Br. Med. J. 3: 756-8, 1972, identified single electric pulses in the ranges of 12 to 15 pulses per minute to increase blood flow response from the lower extremities. More recently, Lindstrom B. et al.: Electrically induced short-lasting tetanus of the calf muscles for prevention of deep vein thrombosis, Br. J. Surg. 69:203-6, 1982, have shown pulse trained stimulation or groups of pulses to be three times more effective than the single pulse group. Early rationale by Lindstrom et al. also identified the posterior muscle pump mechanism to increase venous return. There is also documentation that the muscle stimulation through electrical current as well as sequential compression devices stimulate the release of fibrinolysin to inhibit the coagulation factors of the blood. In one study by Knight and Dawson published in Lancet in 1976, Vol. 1265, it was shown that intermittent pneumatic compression stimulated fibrinolytic activity to such an extent that the incidence of DVT in the legs was reduced.
Katz, Green, Sullivan and Yarkony, Archives of Physical Medicine and Rehabilitation, Vol. 68, July 1987, addressed functional electrical stimulation (FES) of muscles to decrease the incidence of post operative DVT in spinal cord injury patients. Their goal was to demonstrate the value of FES of calf muscles in increasing plasma fibrinolytic activity as well as promoting venous blood flow in the lower extremities. They found a significant increase in plasma fibrinolytic activity. Utilizing doppler ultrasound monitoring of venous flow, they also found a mild to moderate increase in venous return with FES. FES was found not to be as successful as manual compression in promoting emptying of the lower extremities. Stimulation parameters included pulse frequencies of 30 Hertz and pulse widths of 250 microseconds. Stimulation was applied once a minute for a duration of 4 seconds including a 2 second ramp-up. The intensity was sufficient to promote titanic contraction. Superficial electrodes were applied to the anterior and posterior compartments of the calf muscle and energized bilaterally. One electrode was placed over the muscle motor point, and one over the muscle tendon. Sixty minutes of alternating stimulation of the anterior/posterior compartment was achieved using the titanic contractions. Results of this study emphasized the need for FES to be incorporated into a large scale clinical trial in the prevention of DVT in acute spinal cord injury patients.
Research by Merli et al. described in the Archives of Physical Medicine and Rehabilitation, September 1968, evaluated the efficacy of low dose heparin alone or in combination with electrical stimulation in the prevention of DVT in C.sub.2 to T.sub.11 motor complete and incomplete preserved motor, non functional spinal cord patients. The tibialis anterior and gastrocnemius/soleus muscle groups were stimulated bilaterally producing cocontractions of anterior tibialis and gastrocnemius muscles. The stimulation utilized 50 microsecond pulses given at 10 Hertz with a 4 second on and 8 second off cycle for 23 hours daily over a 28 day period. The use of electrical stimulation plus low dose heparin significantly decreased the incidence of DVT compared to other treatments. However, the use of anticoagulants such as heparin can result in increased risk of hemorrhage. Also, there is an inherent inability to use anticoagulants in various neurosurgical and orthopedic situations. Finally, there is a necessity for ongoing blood tests to maintain safe therapeutic levels when using anticoagulants.
Another study by Nicolaides et al., published in Surgery, Vol. 94, pp. 21-5, July 1983, addressed intermittent sequential pneumatic compression of the legs and thromboembolism-deterrent (TED) stockings in the prevention of DVT. The study also included a group whereby electrical stimulation was applied to the calf. Galvanic stimulation with encircling type electrodes were utilized on the gastrosoleus muscle. The rate of stimulation was 12 pulses per minute and the amplitude was adjusted so a brisk plantar-flexion response of the foot was produced with only slight movement at the knee. The results of this study indicated that electrical stimulation was less effective than the regime of intermittent sequential compression and TED stockings.
The problem of DVT has therefore been addressed by Neuro-muscular electrical stimulation. It has not been used for two reasons.
First, it has been assumed that electrical muscle stimulation mimicked the pumping action of volitional muscle contraction, but any substantial increase in venous return had not been quantified and documented. Second, there was considerable stimulus-related pain associated with attempts to use neuro-muscular electrical stimulation (NMES) for DVT protection in the past. This pain was the result of posterior stimulation of the large gastrosoleu muscle and the use of standard pulsed NMES. To be accepted in clinical practice, the issue of pain reduction is important. Application techniques previously identified focused on cocontractions of anterior tibialis and gastrocnemius muscle or stimulation of the gastrocnemius muscle group. Finally, the type of stimulation and selected parameters did not appear to be appropriate to facilitate effective and sensory tolerable contractions of the appropriate muscle group.